[libunwind] [libunwind][PAC] Defang ptrauth's PC in valid CFI range abort (PR #184041)

[Anatoly Trosinenko via cfe-commits]

atrosinenko wrote:

`stripped_value` will be unused variable in the release builds, I guess. By the way, another option could probably be simply wrapping this fragment with `#ifndef _NDEBUG`? Though, I'm not sure whether we do want to skip authentication even in the debug builds or was `ptrauth_auth_and_resign` replaced with `ptrauth_strip` merely for the sake of performance in the release builds (which should not be a problem anymore with `#ifndef _NDEBUG`).

https://github.com/llvm/llvm-project/pull/184041